1. Field of the Invention
The present invention relates to a process cartridge used in an image forming apparatus of an electronic photography copier, a printer or the like, particularly relates to an improvement in a process cartridge of a mode in which a developing cartridge including a developing unit is urged to press to an image carrier cartridge including an image carrier in a state of being positioned thereto and an image forming apparatus using the same.
2. Background Art
In a background art, there is used an image forming apparatus of, for example, an electronic photography system normally arranged with various devices for electronic photography such as a charging unit, a developing unit, a transcribing unit, a cleaning unit at a surrounding of an image carrier of a photosensitive drum or the like and there has already been provided an image forming apparatus in which the various devises having the same service life are summarized to form a process cartridge and when the service life is expired, interchanging operational performance is simplified.
As a process cartridge 500 of this kind, as shown by, for example, FIG. 15, there is normally adopted a system including an image carrier cartridge 501 including an image carrier 511 of a photosensitive drum or the like and a charging unit 512, a cleaning unit 513, and a developing cartridge 502 including a developing unit (including developing function parts of a developing roll and the like) 521 arranged opposedly to the image carrier 511 and a toner replenishing unit 522 for replenishing a toner to the developing unit 521, in which the image carrier cartridge is positioned and fixed by an image forming apparatus main body, relative to the image carrier cartridge 501, the developing cartridge 502 is pivotably positioned to engage with the image carrier cartridge 501 by a pivot shaft (engaging shaft), not illustrated, further, the developing cartridge 502 is urged in a predetermined direction by an urging element of an urge spring or the like, and is urged to press to the image carrier cartridge 501 in a state of positioning the developing cartridge 502 thereto (for example, JP-A-2004-37638 and Japanese Patent No. 3534104).
However, according to the process cartridge described in JP-A-2004-37638 and Japanese Patent No. 3534104, the developing cartridge 502 is constituted by integrating the toner replenishing unit 522 to the developing unit 521 and therefore, when a weight of the toner replenishing unit 522, that is, a toner containing amount is changed, a press urge force of the developing cartridge 502 to the image carrier cartridge 501 is varied and there is a concern of bringing about a disturbance in an image.
That is, in the case of setting the press urge force of the developing cartridge 502 to be proper when a toner containing amount of the toner replenishing unit 522 is full, when the toner containing amount becomes small, the press urge force becomes deficient and there is a concern of separating the developing roll of the developing unit 521 from the image carrier 511.
Conversely, in the case of setting the press urge force of the developing cartridge 502 to be proper when the toner containing amount of the toner replenishing unit 522 is small, when the toner containing amount is full, the press urge force of the developing cartridge 502 becomes excessively large, and there is a concern that a gap adjusting spacer between the image carrier cartridge 501 and the developing cartridge 502 is deformed, or a rotational load of the image carrier 511 becomes excessively heavy.
Further, JP-A-7-146634 proposes to make the press urge force of the developing cartridge constant by devising a point of engaging the image carrier cartridge and the developing cartridge (a structure of installing the point of engaging the two units on a perpendicular line passing a gravitational center of the developing cartridge or a vicinity thereof).
However, although the technology described in JP-A-7-146634 is applicable to a mode in which a position of the gravitational center of the developing cartridge is not varied, in a number of modes in which the developing unit and the toner replenishing unit are integrated in the developing cartridge, the position per se of the gravitational center of the developing cartridge is varied and therefore, the situation of varying the press urge force of the developing cartridge cannot effectively be avoided.